1. Field of the Invention
The present invention relates to a low pressure chemical vapor deposition (LPCVD) apparatus for depositing a thin film on a substrate, and more particularly, to a low pressure chemical vapor deposition (LPCVD) apparatus which includes means for pumping out unreacted gas and for curtailing further reaction involving the remaining unreacted gas by attaching components of the unreacted gas which remain in a positive or negative ionic condition, to a door plate, so as to form on the substrate a film having excellent uniformity, and to remove particulate matter from within the reactor.
2. Description of the Related Art
In general, chemical vapor deposition (hereinafter referred to as CVD) forms thin films on the surface of a substrate by decomposition of gaseous compounds introduced into a reactor. However, a conventional CVD system has a disadvantage that some reactant gas components which remain in a positive or negative ionic condition are not deposited on the substrate to become part of a respective thin film on the substrate, but remain in the chamber of the reactor as particulate matter unnecessary to deposit the film. Each of such components include NH.sub.4 Cl and Si.sub.x P.sub.y.
Accordingly, it is difficult to deposit the film with excellent uniformity.
In a conventional low pressure chemical vapor deposition (hereinafter referred to as LPCVD) apparatus, the reactant gas is introduced at the one end of the chamber of the reactor and pumped out at the opposite end of the chamber of the reactor, using a pump, so that the CVD film is directly deposited from the gas phase within the chamber onto the surface of a heated substrate positioned within the chamber.
After the film has been deposited to a desired thickness, the unreacted gas remaining in the chamber within the quartz tube which forms the peripheral sidewall of the reactor is pumped out using the pump, so that the chamber within the quartz tube maintains a low pressure. By this means, particulate matter is removed from a conventional LPCVD apparatus.
The LPCVD apparatus has a disadvantage that the deposited film simultaneously coats both the substrate on which it is intended that a film be formed, and the inside of the tube for example, the inner peripheral wall of the quartz tube or the paddle which is conventionally provided, so that unreacted gas remaining in the chamber is reacted at a fabrication step thereafter.
Therefore, the unreacted gas functions as a major source of particulate matter which becomes deposited onto the surface of the substrate, such as a wafer disposed in the chamber within the quartz tube.
In another conventional apparatus, after the CVD film is deposited to a desired thickness onto the surface of the wafer in the chamber within the quartz tube, N.sub.2 gas is introduced into the chamber and the unreacted gas remaining in the chamber within the quartz tube is pumped out.
Then, the particulate matter is removed.
However, in this conventional apparatus, the N.sub.2 gas is comparatively cold and therefore facilitates combinations among components of the unreacted gases remaining in the quartz tube, so that particulate matter is produced.
Therefore, it is a disadvantage that after the performance of the actual deposition step of the conventional CVD process, another step needs to be performed so that the films, which are deposited, are deposited with excellent uniformity, such additional step being required for reducing the particulate matter.